Method of manufacturing positive active material for batteries

ABSTRACT

Heavy-load discharge characteristics of a primary battery are improved. Alternatively, the high-rate discharge characteristics of a secondary battery are improved. This is accomplished by employing manganese oxides as the positive active material on which a surface modified layer is formed. The surface modified layer consists of an oxide of at least one element selected from the group consisting of titanium, cobalt, nickel, strontium, lanthanum and its compound added mainly with a compound made of manganese oxide on the surface of manganese oxide powder consisting of manganese dioxide or a complex oxide of manganese and lithium. This is accomplished by using a solution of salt of at least one element selected from the group consisting of titanium, cobalt, nickel, strontium, and lanthanum to which a manganese salt and a solution, to which a solution of manganese salt are added.

This application is a division of application Ser. No. 08/791,586, filedJan. 31, 1997, now U.S. Pat. No. 5,744,266.

FIELD OF THE INVENTION

The present invention relates to alkaline-manganese batteries orlithium-ion secondary batteries using the powder of manganese oxides,consisting of manganese dioxide or double oxide of manganese andlithium, on which a surface modification layer is formed as a positiveactive material, and a method of manufactuing said positive activematerial for the batteries made of manganese oxide powder on which asurface-modification layer is formed.

BACKGROUND OF THE INVENTION

Various primary batteries employing manganese dioxide as the positiveactive material such as the carbon-zinc dry batteries, called Leclanchetype or zinc chloride type batteries, employing neutral salts ofammonium chloride or zinc chloride as electrolytes, have been wellknown. Also, alkaline manganese batteries employing potassium hydroxideas the electrolyte, and Li/MnO₂ system primary batteries belonging toorganic electrolyte lithium batteries, employing manganese dioxide asthe positive active material have been well-known.

On the other hand, lithium-ion secondary batteries which can behigh-energy density small size rechargeable batteries in the nextgeneration have also been known. These batteries employ positive andnegative electrodes made of a host material repeating intercalation anddeintercalation of lithium-ions by charging and discharging, realizingthe heavy load discharge, rapid charge, long cyclic life, etc.

Presently, as the host material, a double oxide consisting of cobalt andlithium, or LiCoO₂, is used as the positive electrode, while carbon isgenerally used as the negative electrode. However, because of theunstable world supply from the high cost and omnipresence of positiveelectrode material or cobalt, this can now be replaced by LiMnO₂ orLiMn₂ O₄ which are double oxides of manganese and lithium.

As the result of recent power consumption decreases realized by thesignificant advancement of semiconductor electronics technology, anumber of portable electric and electronic apparatuses have beendeveloped and practically used. Various audio visual (AV) apparatusesincluding the strobe-flash light for still-camera, portable shaver,headphone stereo-player, and liquid crystal display-television (LCD-TV)are typical of these advancements wherein the demand and the use ofalkaline manganese batteries having excellent continuous dischargecharacteristics is now expanding very rapidly.

However, in contrast to these tendencies, increases of power consumptionby the multi-functional portable apparatuses have been obvious. Forexample, in the cases of portable data acquisition (PDA) such asportable telephone and facsimile, notebook personal computer andcamcorder, better battery performance taking heavy and continuous loadshas been demanded.

Therefore, new built-in type secondary batteries such as thehigh-capacity nickel-cadmium system, nickel-metal hydride system, orlithium ion type batteries have been developed. At the same time, thedemand for alkaline manganese batteries capable of continuous dischargeat heavy load working as supplementary power sources is increasing.

When batteries are continuously discharged, decreases of operatingvoltages due to polarization are generally inevitable in proportion tothe increase of load current. Thus, the end voltage is reached beforethe active materials of positive and negative electrodes are fullyreacted so that the ultimate efficiency of active material remains low.

The polarization-based lowering of the operation voltage of dischargingcells could be attributed to three reasons, including the resistancepolarization due to the electrical ohmic resistance produced in theouter and inner cell, the activation polarization due to the chargetransfer reaction, and the concentration polarization due to thediffusion control process of reaction materials or products.

Conventionally, in order to improve the continuous heavy load dischargecharacteristics of alkaline manganese batteries, the amount ofelectrolytic manganese dioxide (hereinafter, abbreviated as "EMD")contained in the positive active material is increased, a highconductivity graphite is used as the conductive material in the positiveelectrode mix, lowering the amount of additives, or a thin separator inwhich very fine fibers are uniformly distributed is employed.

Other than those discussed above, improvements introducing a gellingagent or a zinc corrosion inhibitor in the negative electrode have beenconsidered effective. In addition to this, the employment of a positiveelectrode of larger polarization as compared to the zinc in the negativeelectrode has also been considered.

For example, as shown in U.S. Pat. Nos. 5,277,890 and 5,391,365, methodsusing EMD powder by expanding its specific surface by formingfilament-like protrusions thereon by using a chemical synthetic methodprecipitating MnO₂ thereon have been developed. In addition to this, amethod using a positive electrode to which powder of anatase titaniumdioxide is added and mixed as shown in U.S. Pat. 5,342,712 has beendisclosed.

Although these inventions have been slightly effective in increasing thebattery service-life at continuous discharge and decreasing thepolarization compared to a case where a conventional positive electrodemade of EMD powder only is used, these had been minimally effective whena heavier load had to be discharged continuously.

SUMMARY OF THE INVENTION

Alkaline-manganese batteries and lithium-ion secondary batteries aredisclosed having longer service lives at heavier loads and continuousdischarge. These batteries are made of powder of manganese oxidesemploying manganese dioxide or double oxide of manganese and lithiumacting as the positive active material on which surface modificationlayers are formed, and a method of manufacturing the positive activematerial for these batteries is disclosed.

MnO₂ powder or highly active EMD powder may be used as the positiveactive material of alkaline manganese batteries. Since the electronicconductivity of EMD powder is not necessarily very high, a conductiveagent consisting mainly of graphite having no direct contribution to itsconductivity had to be added up to an amount of 10 wt %.

The main discharge reaction of MnO₂ acting as the positive activematerial in the alkaline electrolyte, can be expressed by a uniformsolid-phase reaction shown in Eq. (1), having appropriate conductivityof active material, and also the employment of the material minimizingthe concentration polarization, due to the ion diffusion within thesolid phase.

    MnO.sub.2 +H.sub.2 O+e→MnOOH+OH                     (1)

The positive electrode potential is expressed by Eq. (2). ##EQU1##

As shown above, in accordance with an exemplary embodiment of thepresent invention, batteries are offered having excellent continuousdischarge characteristics realized even when a heavy load is applied, byemploying manganese oxide consisting of EMD powder whose surface issuitably modified as the positive active material, having a very littleohmic loss due to the electric resistance, and particularly having asmall concentration polarization.

More specifically, batteries employing a positive active materialconsisting of manganese oxide powder having a surface modified bydepositing thereon a layer of a compound consisting mainly of oxide ofat least one element selected from the group consisting of titanium(Ti), cobalt (Co), nickel (Ni), strontium (Sr), and lanthanum (La) aredisclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a flow-chart of the manufacturing process of the positiveactive material of the present invention consisting of manganese oxidehaving a surface modified layer.

FIG. 2 shows examples of comparative transition curves of singleelectrode potentials of positive active materials made of surfacemodified by the present invention and conventional untreated EMD powderplaced in an alkaline electrolyte.

FIG. 3 shows a relationship between the amount of titanium contained inthe EMD powder of the present invention whose surface is modified, theelectric conductivity, and the gravimetric capacity density thereof.

FIG. 4 shows a half vertical cross-section of a LR6(AA) size alkinemanganese battery which is a typical example of the battery of thepresent invention.

FIG. 5 shows a relationship between the discharge characteristics ofalkaline manganese batteries employing positive active material of thepresent invention having a surface layer modified by a nickel compoundwith those obtained by employing conventional positive active materialmade of untreated EMD powder.

FIG. 6 shows a relationship between the total amount of Co and/or Nicontained in the modified surface layer of EMD powder and the dischargecapacity ratio.

FIG. 7 shows the discharge characteristics of alkaline manganesebatteries employing the positive active material of the presentinvention having a surface layer modified by La compound, compared withthose obtained by employing a positive active material usingconventional untreated EMD powder.

FIG. 8 shows a relationship between the total amount of Sr and/or Lacontained in the surface modified layer of EMD powder and the possiblenumber of pulse discharges.

FIG. 9 shows a cross-sectional view of a coin type lithium ion secondarycell which is another typical example of the battery of the presentinvention.

FIG. 10 shows a cross-sectional view of R20(D) size zinc chloride typecarbon-zinc dry cell which is another typical example of the battery ofthe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A typical structure of the alkaline manganese battery of the presentinvention and a method of manufacturing the positive active material forthe same are now explained here by referring to the attached drawingsand tables.

<Embodiment-1>

The EMD block electrodeposited on a Ti anode held in a high-temperaturemanganese sulphate bath, at a temperature of more than 90° C., is firstpeeled off from the Ti node. After coarsely crashing and washing theblocks of EMD, it is pulverized by a roller-mill to obtain EMD powderhaving an average grain diameter of 50 μm, and this is dried by aconventional method to obtain EMD powder.

Then the surface of EMD powder is subjected to a modification treatmentaccording to the flow-chart of the manufacturing process shown in FIG.1.

(1) Mixing . . . 300 grams of the EMD powder is weighed, mixed, anddispersed in an aqueous solution of 3.0 liters containing titaniumsulfate which is neutral or of H₂ SO₄ acidity .

(2) Treatment . . . By heating the solution having said EMD powderdispersed within, a Ti compound is deposited and coated on the surfaceof EMD powder, modifying the surface thereof. A treatment temperature of80° C. is used in this case. The treatment can be accelerated bybubbling into the solution the oxidizing gas such as air, oxygen, orozone containing the air or oxygen, or by adding an oxidizing agent suchas sodium perchlorate (NaClO₃) or sodium persulfate (Na₂ S₂ O₈.2H₂ O)thereto.

(3) Filtration . . . The EMD powder whose surface is modified isfiltrated in this process, and this process may be replaced by adecantation of the supernatant is solution, and this is shifted into thesuccessful washing process.

(4) Washing . . . Pouring and stiring of pure water, and removal of thesupernatant solution is repeated several times.

(5) Neutralization . . . By adding drops of an aqueous sodium hydroxidesolution in a state of agitation, the pH thereof is stabilized into arange from 6.0 to 8.0.

(6) Drying . . . The product is dried for 24 hours at 80° C.

In addition to above, the surface modification shown in the processes of(1)-(3), may be replaced by processes of coarse crushing of EMD grain,(4) Washing, (5) Neutralization, and a process of Pulverizing.Furthermore, stabilizing and improving the characteristics of modifiedEMD are possible by applying a heat treatment in an aqueous sulfuricacid aqueous solution after Treatment (2).

The electric conductivity, moistures, and the discharge capacity ratiosof positive active materials determined by the addition of sulfuric acid(H₂ SO₄) to Ti(SO₄)₂ aqueous solution and the types of oxidizing agentare listed in Table 1 shown below.

                                      TABLE 1    __________________________________________________________________________    Sample No.              1  2  3  4  5  6  7  3  9  10 11    __________________________________________________________________________    Composition of    Treatment Solution    Ti (SO.sub.4).sub.2 (mol/l)              -- 0.2                    0.2                       0.2                          0.2                             0.2                                0.2                                   -- 0.2                                         0.2                                            0.2    H.sub.2 SO.sub.4  (mol/l)              -- 2.0                    2.0                       2.0                          2.0                             2.0                                2.0                                   2.0                                      -- -- --    Oxidizing Agent    Air (ml/min)              -- -- -- -- 50 -- -- -- -- 50 --    O.sub.2  (ml/min)              -- -- -- -- -- 50 -- -- -- -- --    O.sub.3  (ml/min)              -- -- -- -- -- -- 50 -- -- -- --    Na.sub.2 ClO.sub.3              -- ∘                    -- -- -- -- -- -- ∘                                         -- --    Na.sub.2 S.sub.2 O.sub.8 2H.sub.2 O              -- -- ∘                       -- -- -- -- -- -- -- --    Electric Conductivity              13.7                 995                    990                       800                          930                             950                                950                                   14.0                                      810                                         870                                            570    (×10.sup.-3 S/cm)    Moisture (wt %)              4.58                 4.90                    4.80                       4.20                          4.55                             4.35                                4.43                                   4.12                                      4.05                                         4.32                                            4.55    Discharge Capacity              100                 107                    106                       105                          107                             107                                106                                   101                                      105                                         106                                            104    Ratio    __________________________________________________________________________

In Table 1, the ozone (O₃) content in the oxidizing agent causes directbubbling of oxygen (O₂), including the O₃ generated by the flow-in of O₂into the ozonizer, at a flow rate of 50 ml/min into the treatmentsolution.

The electric conductivity is determined by placing the sample powder ofpredetermined volume in a die made of PTFE, and by measuring theterminal DC resistance at a state where a pressure of 3 t/cm² isapplied. The moisture is determined by subtracting the weight of thesample heated and dehydrated at 500° C. from the weight of the sampledried at 105° C.

In addition to these determinations, preparing a workng positiveelectrode by pressing a mixture of sample powder of 10 weight partsmixed with acetylene black of 1 weight part onto a platinum (Pt) plate,using a counter electrode made of Pt plate and a reference electrodemade of Hg/HgO, and by measuring the capacity of the positive electrodepotential reaching to a potential of -300 mV from the referenceelectrode potential, applying a constant current of 10 mA per one gramof the sample in an alkaline electrolyte consisting of 40 wt % potassiumhydroxide (KOH) aqueous solution, dissolving 3.0 wt % zinc oxide (ZnO),and the capacity ratios of each sample are derived, defining thecapacity of the EMD powder sample No. 1 as 100.

Here, the discharge end potential of -300 mV is employed as a potentialcorresponding to the discharge ending voltage of a 0.9 V alkalinemanganese battery.

Table 1 shows that all of the electric conductivity of Sample Nos. 2-7and Nos. 9-10 obtained by treating the EMD powder in a Ti(SO₄)₂ aqueoussolution are higher by about two orders compared to that of untreatedEMD powder Sample No. 1. Among these, the tendency for slightly higherelectric conductivity is observed when H₂ SO₄ is added to the treatmentsolution (Sample Nos. 2-7). These tendencies are obvious, particularlywhen H₂ SO₄ is added together with the oxidizing agent (Sample Nos. 2,3, 5, 6, and 7). In addition to these, no particular differences basedon the type of oxidizing agent have been observed.

The electron-microscopic observations made on the surfaces of untreatedEMD powder of Sample No. 1 and those of Sample No. 2, obtained bytreating the EMD powder in an H₂ SO₄ acidity Ti(SO₄)₂ aqueous solutionbeing added by an Na₂ ClO₃ oxidizing agent, showed a little surfaceirregularity for Sample No. 1 and less irregularity for Sample No. 2.This can be attributed to the irregularities smoothed out by thedeposition.

Since a moisture of up to 5 wt. % is usually contained in EMD powder,the content of MnO₂ and the electric conductivity could be increased bythe removal of moisture which could be done by applying a heattreatment. However, it is sacrificing capacity by the positive electrodepotential being lowered by the discharge in the alkaline electrolyte.

Table 1 shows that not only the electric conductivity is improved by twoorders, but a significantly increased discharge capacity can be obtainedwithout reducing the moisture by using the EMD powder on which a surfacemodified layer is formed by using a Ti compound.

It has been confirmed by using an element analysis method that thecontent of titanium in Sample No. 2 is around 1.8 wt. %. Thus, this isattributed to the EMD powder whose entire or partial surface is modifiedby the thin deposition of the titanium compound consisting essentiallyof titanium oxide. Although the exact determination of the thickness ofthe surface modified layer is impossible even with an X-ray diffractionmethod because of its extremely small thickness. However, theeffectiveness of the surface modified layer is obvious.

FIG. 2 shows two discharge characteristics of unipolar electrodepotential in an alkaline electrolyte obtained with Sample Nos. 1 and 2.

In FIG. 2, while a rapid potential decrease of Sample No. 1 employinguntreated EMD powder at the end of discharge is observed, a gentlepotential decrease of Sample No. 2 employing the EMD powder on which asurface layer modified by a titanium compound is found, and this can beattributed to the significant improvement in capacity. In addition, noparticular surface modification effect has been observed with Sample No.8 employing the EMD powder treated by sulfuric acid, and very littlechange is observed with Sample No. 1.

<Embodiment-2>

By adjusting the concentration of sulfuric acid in the treatmentsolution to 2.0 mol/l various surface modified EMD powders of differenttitanium content are prepared in accordance with Embodiment-1 bychanging the concentration of Ti(SO₄)₂ and the treatment condition.

From these, the gravimetric capacity densities (mAh/g) are determinedfrom the measurements of electrical conductivity and the singleelectrode discharge tests, and the results of these are shown in FIG. 3.

FIG. 3 also shows a steady increase in the electric conductivity inproportion to the increase of Ti content in contrast to that of SampleNo. 1 which is fixed at 13.7×10-3 S/cm, and also shows a near saturationof electric conductivity at a point exceeding 0.1 wt. %. On the otherhand, the gravimetric capacity density is found optimum with a titaniumcontent in a range from 0.1-5.0 wt. %.

<Embodiment-3>

Various positive active materials whose surfaces are modified areprepared by adding salts of manganese, nickel, or cobalt to the H₂ SO₄acidity Ti(SO₄)2 treatment solution according to Embodiment-1, and theelectric conductivity, moistures, and the apparent densities thereof aremeasured. Then, after preparing various LR6 (AA) type alkaline manganesebatteries, the discharge capacity ratios at heavy and medium loads aredetermined.

A cross-section of the experimental, LR6 size alkaline manganese batteryis shown in FIG. 4 wherein the cap 1A made of nickel plated steel actingas its positive terminal is integrally molded, and conductive coating IBmade of carbon paint is coated on the inner wall of the positive can 1.

Then, manganese oxide made either of untreated EMD powder or varioussurface modified EMD powder mixed with graphite, at a weight ratio of 9to 1, is press-molded into a shape of cylinder, and four of thecylinders are inserted into said positive can 1, and positive electrodemold 2 is press-molded on the inner wall of positive can 1.

Inserting cylinder-shaped separator 3 and bottom plate 3A withinpositive electrode mold 2, gel negative electrode 4, prepared bydispersing the zinc powder of 2 weight parts in a viscous solution of 1weight part and dissolving a gelling agent made of carboxymethylcellulose (CMC) or polysodium acrylate or others injected into saidalkaline electrolyte.

Then, negative electrode terminal 6 made of nickel-plated steel on whichbrass current collector 5 is welded and washer 7 are integrated byplastic sealer 8, this unit is inserted into gel negative electrode 4.Where sealer 8 is placed on groove 1C formed by inwardly curling theopening of positive can 1, the upper edge of said can 1 is curled,inwardly sealing the can. This cell assembly process is ended bysticking label 9 thereon at the end.

The discharge test of each cell is performed under a heavy load giving aconstant current of 1000 mA and under a medium load giving a constantresistance of 10 ohms continuous discharge, obtaining a discharge-endvoltage of 0.9 V in both cases. Table 1 shows a tabulation of dischargeperiods wherein the discharge period obtained by Sample No. 1 cell,employing a positive active material made of untreated EMD powder, isdefined as 100, and those of other cells, each employing positive activematerial made of treated EMD powder of which surface layer is modified,are defined as the ratios of those to that of Sample No. 1.

The results of these are tabulated in Table 2.

                                      TABLE 2    __________________________________________________________________________    Sample No.              1  2  12 13 14 15 16 17 18 19 20    __________________________________________________________________________    Composition of    Treatment Solution    Ti (SO.sub.4).sub.2 (mol/l)              -- 0.2                    0.2                       0.2                          0.2                             0.2                                0.2                                   0.2                                      0.2                                         0.2                                            0.2    H.sub.2 SO.sub.4  (mol/l)              -- 2.0                    2.0                       2.0                          2.0                             2.0                                2.0                                   2.0                                      2.0                                         2.0                                            2.0    MnSO.sub.4 (mol/l)              -- -- 0.2                       -- -- 0.2                                0.2                                   -- 0.2                                         0.2                                            0.2    CoSO.sub.4 (mol/l)              -- -- -- 0.2                          -- 0.2                                -- 0.2                                      0.2                                         0.2                                            0.2    NiSO.sub.4 (mol/l)              -- -- -- -- 0.2                             -- 0.2                                   0.2                                      0.2                                         0.2                                            0.2    Kind of Oxidizing    Agent    Air (ml/min)              -- -- -- -- -- -- -- -- -- 50 --    O.sub.2  (ml/min)              -- -- -- -- -- -- -- -- -- -- 50    Na.sub.2 ClO.sub.3              -- ∘                    ∘                       ∘                          ∘                             ∘                                ∘                                   ∘                                      ∘                                         -- --    Electrical Conductivity              13.7                 995                    990                       990                          930                             950                                950                                   950                                      970                                         980                                            920    (×10.sup.-3 S/cm)    Moisture (wt %)              4.58                 4.9                    4.2                       4.2                          4.55                             4.15                                4.13                                   4.12                                      4.05                                         4.12                                            4.15    Apparent Density              2.67                 2.60                    2.92                       2.65                          2.66                             2.93                                2.90                                   2.64                                      2.96                                         2.87                                            2.89    (g/cm.sup.3)    Heavy Load              100                 100                    100                       105                          105                             103                                103                                   105                                      105                                         105                                            105    Discharge Capacity    Ratio    Medium Load              100                 107                    106                       105                          105                             107                                106                                   102                                      105                                         106                                            104    Discharge Capacity    Ratio    __________________________________________________________________________

While the electric conductivity of untreated EMD powder of Sample No. 1is 13.7×10-3 S/cm, those of the others using the treatment which includetitanium salt solution containing either the salt of manganese, nickel,cobalt, etc., are higher by two orders. Moistures of Sample Nos. 12, 15,16, 18, 19 and 20 added with manganese salt are known to be slightlyless than that of Sample No. 1, and there is also a slight increase ofthe apparent densities.

These results can be attributed to a possible deposition of chemicalmanganese dioxide (CMD) having a fundamentally low moisture (less than1.0 %) on EMD simultaneously with the deposition of a compoundconsisting mainly of titanium oxide.

Considerably improved heavy load discharge characteristics are foundwith Sample Nos. 13-20 depositing a cobalt and/or-nickel compound mixedwith a titanium compound. The considerable improvements of heavy loaddischarge characteristics cannot only be explained by the noblerpotential of CoOOH and/or NiOOH of cobalt and/or nickel oxide depositedtogether with the titanium oxide, but it can probably be explained bythe suppressed concentration polarization together with the suppressedresistance polarization taking place during the discharge.

Moreover, since the electric conductivity of surface modified EMIincluding the titanium compound is improved, the content of conductiveagent such as graphite could be reduced at a level less than 10 wt. %.However, the dependency on the type of oxidizing agents has not beenclearly shown.

<Embodiment-4>

In Embodiment-3 described above, the improvements of heavy loaddischarge characteristics of alkaline manganese batteries by employingthe EMD powder whose surface is modified by a titanium compound togetherwith a compound of cobalt and/or nickel which have previously beenexplained.

Therefore, in Embodiment-4 shown here, LR6 size alkaline manganesebatteries, utilizing a positive active material formed on the EMD powderwhose surface layer is modified, are prepared in accordance withEmbodiment-1, using a solution of cobalt salt and/or nickel salt, orcobalt salt and/or nickel salt including the manganese salt excludingthe use of titanium salt in the treatment solution.

All of these batteries are subjected to a continuous discharge testsupplying a constant current of 1500 mA (obtaining an end voltage of 0.9V), and the discharge capacity ratios of those batteries, defining thatobtained by Sample No. 1 using untreated EMD powder as 100, aredetermined. The results of those tests are shown in Tables 3, 4, and

                                      TABLE 3    __________________________________________________________________________    Sample No.              1  21 22 23 24 25 26 27 28 29    __________________________________________________________________________    Composition of    Treatment Solution    H.sub.2 SO.sub.4  (mol/l)              -- 2.0                    2.0                       2.0                          2.0                             2.0                                2.0                                   -- -- --    CoSO.sub.4 (mol/l)              -- 0.2                    0.2                       0.2                          0.2                             0.2                                0.2                                   0.2                                      0.2                                         0.2    Oxidizing Agent    Air (ml/min)              -- -- -- -- 50 -- -- -- -- 50    O.sub.2  (ml/min)              -- -- -- -- -- 50 -- -- -- --    O.sub.3  (ml/min)              -- -- -- -- -- -- 50 -- -- --    Na.sub.2 ClO.sub.3              -- -- ∘                       -- -- -- -- -- ∘                                         --    Na.sub.2 S.sub.2 O.sub.8 2H.sub.2 O              -- -- -- ∘                          -- -- -- -- -- --    Discharge Capacity              100                 104                    106                       106                          105                             104                                106                                   104                                      104                                         106    Ratio    __________________________________________________________________________

                                      TABLE 4    __________________________________________________________________________    Sample No.              1  30 31 32 33 34 35 36 37 38    __________________________________________________________________________    Composition of    Treatment Solution    H.sub.2 SO.sub.4  (mol/l)              -- 2.0                    2.0                       2.0                          2.0                             2.0                                2.0                                   -- -- --    CoSO.sub.4 (mol/l)              -- 0.2                    0.2                       0.2                          0.2                             0.2                                0.2                                   0.2                                      0.2                                         0.2    Kind of    Oxidizing Agent    Air (ml/min)              -- -- -- -- 50 -- -- -- -- 50    O.sub.2  (ml/min)              -- -- -- -- -- 50 -- -- -- --    O.sub.3  (ml/min)              -- -- -- -- -- -- 50 -- -- --    Na.sub.2 ClO.sub.3              -- -- ∘                       -- -- -- -- -- ∘                                         --    Na.sub.2 S.sub.2 O.sub.8.2H.sub.2 O              -- -- -- ∘                          -- -- -- -- -- --    Discharge Capacity              100                 105                    107                       106                          107                             107                                106                                   104                                      105                                         106    Ratio    __________________________________________________________________________

                                      TABLE 5    __________________________________________________________________________    Sample No.              1  39 40 41 42 43 44 45 46 47 48    __________________________________________________________________________    Composition of    Treatment Solution    H.sub.2 SO.sub.4  (mol/l)              -- 2.0                    2.0                       2.0                          2.0                             2.0                                2.0                                   2.0                                      2.0                                         -- --    CoSO.sub.4 (mol/l)              -- 0.2                    -- 0.2                          0.2                             0.2                                0.2                                   0.2                                      0.2                                         0.2                                            0.2    NiSO.sub.4 (mol/l)              -- 0.2                    0.2                       -- 0.2                             0.2                                0.2                                   0.2                                      0.2                                         0.2                                            0.2    MnSO.sub.4 (mol/l)              -- -- 0.2                       0.2                          0.2                             0.2                                0.2                                   0.2                                      0.2                                         -- 0.2    Kind of Oxidizing    Agent    Air (ml/min)              -- -- -- -- -- -- -- -- -- 50 --    O.sub.2  (ml/min)              -- -- -- -- -- -- -- -- -- -- 50    O.sub.3  (ml/min)              -- -- -- -- -- -- -- -- 50 -- --    Na.sub.2 ClO.sub.3              -- ∘                    ∘                       ∘                          ∘                             ∘                                ∘                                   ∘                                      ∘                                         -- --    Na.sub.2 S.sub.2 O.sub.8.2H.sub.2 O              -- -- -- -- -- ∘                                -- -- -- -- --    Apparent Density              2.67                 2.65                    3.03                       2.98                          2.92                             2.92                                2.97                                   3.00                                      3.01                                         2.66                                            2.88    (g/cm.sup.3)    Discharge Capacity              100                 106                    105                       105                          106                             107                                106                                   107                                      105                                         104                                            105    Ratio    __________________________________________________________________________

Characteristic examples of 1500 mA constant current continuous dischargecharacteristics of an alkaline manganese battery using the positiveactive material employed by Sample No. 1 and Sample No. 30 are shown inFIG. 5.

FIG. 5 shows a higher discharge capacity up to a discharge end voltageof 0.9 V since the discharge voltage is improved by using EMD powderwhose surface layer is modified by a nickel compound made mainly ofnickel oxide, which could be NiOOH, used as the positive electrode.

In addition, no noticeable difference between the points at which thedischarge capacity is lost and at which the discharge voltage is rapidlydecreased has been observed.

In the cases where the surface of EMD powder is modified by introducinga Co and/or Ni compound or a Co and/or Ni compound containing a Mncompound into the treatment solution, instances of a slightly higherdischarge voltage and discharge capacity ratio have been observed whenthe treatment solution of H₂ SO₄ acidity (Samples Nos. 21-26, 30-35, and39-46) is used compared with the case where the treatment solution of noH₂ SO₄, acidity is used.

Moreover, though no particular effect of the oxidizing agent has beenobserved in this case, slightly improved discharge characteristicsrealized by the introduction of an oxidizing agent in the treatmentprocess have been seen.

In this embodiment also, like in the case of Embodiment-3, the higherapparent density realized by the introduction of manganese salt in thetreatment solution has been observed.

FIG. 6 shows the relationship between the discharge capacity as a ratioof a positive electrode made of EMD powder whose surface is modified bythe deposition of Co and/or Ni compound and the total contents of Coand/or Ni. Like in the cases of Embodiments-1 and -2, the dischargecapacity ratios are determined by conducting single electrode dischargetests in an alkaline electrolyte and defining the ratio obtained by theuntreated EMD powder as 100. FIG. 6 also shows the discharge capacityratios of every EMD powder whose surface layers are modified by using aCo and/or Ni compound, and these are higher than that (240 mAh/g) ofuntreated EMD powder. It shows the effectiveness of the total contentsof Co and/or Ni in a range from 0.1-10.0 wt %. in these cases.

Electron-microscopic observations made on the surface of EMD powdermodified by a Co and/or Ni compound and a Co and/or Ni compoundcontaining a Mn compound, like the case where the surface is modified bya Ti compound, have proved the order of surface irregularities less thanthose observed on the untreated EMD powder. Moreover, like the cases ofEmbodiments -3 and -4, the higher apparent densities of surface modifiedEMD powder containing a Mn compound (Sample Nos. 40-46 and 48) areobserved.

<Embodiment-5>

Embodiments 1-4 have proved the effectiveness of EMD powder whosesurfaces are modified by forming a Ti compound or a Co (cobalt) and/orNi (nickel) compound and by forming a Ti compound containing Mn or Coand/or Ni compound. In Embodiment -5, the effects of the surfacemodification by using a Sr (strontium) and/or La (lanthanum) compound,and by using a Sr (strontium) and/or La (lanthanum) compound containingMn compound are shown.

Like the case of Embodiment -1, various LR6-size alkli manganesebatteries employing the EMD powder whose surface is modified by a Sr(strontium) and/or La (lanthanum) compound, and by a Sr (strontium)and/or La (lanthanum) compound containing a Mn compound as its positiveactive material, are prepared, and these are subjected to a pulsedischarge test.

The pulse discharge test is a test simulating a strobe flash for astill-camera where the discharge is repeated for 15 sec., on a constantresistance of 1.8 ohms allowing a rest period of 45 sec., the number ofthe discharges is counted until an end voltage of 0.9 V is reached. Thenumber of pulse discharges obtained by the cell of Sample No. 1employing untreated EMD powder is defined as 100, the ratio of thenumber of pulse discharges obtained by a cell employing surface modifiedEMD powder is expressed by the discharge capacity ratio. These resultsare shown in Tables 6, 7, and 8.

Some examples of the 1500 mA constant current discharge characteristicsof LR6-size alkaline manganese batteries prepared by employing untreatedEMD powder, and the ones employing the positive active materialemploying the EMD powder (Sample No. 58) whose surface is modified by aLa compound are shown in FIG. 7.

                                      TABLE 6    __________________________________________________________________________    Sample No.              1  49 50 51 52 53 54 55 56 57    __________________________________________________________________________    Composition of    Treatment Solution    H.sub.2 SO.sub.4  (mol/l)              -- 2.0                    2.0                       2.0                          2.0                             2.0                                2.0                                   -- -- --    SrSO.sub.4 (mol/l)              -- 0.2                    0.2                       0.2                          0.2                             0.2                                0.2                                   0.2                                      0.2                                         0.2    Oxidizing Agent    Air (ml/min)              -- -- -- -- 50 -- -- -- 50 --    O.sub.2  (ml/min)              -- -- -- -- -- 50 -- -- -- --    O.sub.3  (ml/min)              -- -- -- -- -- -- 50 -- -- --    Na.sub.2 ClO.sub.3              -- ∘                    -- -- -- -- -- ∘                                      -- --    Na.sub.2 S.sub.2 O.sub.8 2H.sub.2 O              -- -- ∘                       -- -- -- -- -- -- --    Discharge Capacity              100                 106                    106                       104                          105                             104                                104                                   105                                      106                                         103    Ratio    __________________________________________________________________________

                                      TABLE 7    __________________________________________________________________________    Sample No.              1  58 59 60 61 62 63 64 65 66    __________________________________________________________________________    Composition of    Treatment Solution    H.sub.2 SO.sub.4  (mol/l)              -- 2.0                    2.0                       2.0                          2.0                             2.0                                2.0                                   -- -- --    LaSO.sub.4 (mol/l)              -- 0.2                    0.2                       0.2                          0.2                             0.2                                0.2                                   0.2                                      0.2                                         0.2    Oxidizing Agent    Air (ml/min)              -- -- -- -- 50 -- -- -- 50 --    O.sub.2  (ml/min)              -- -- -- -- -- 50 -- -- -- --    O.sub.3  (ml/min)              -- -- -- -- -- -- 50 -- -- --    Na.sub.2 ClO.sub.3              -- ∘                    -- -- -- -- -- ∘                                      -- --    Na.sub.2 S.sub.2 O.sub.8 2H.sub.2 O              -- -- ∘                       -- -- -- -- -- -- --    Discharge Capacity              100                 107                    106                       105                          107                             107                                106                                   105                                      106                                         104    Ratio    __________________________________________________________________________

Tables 6, 7 and 8 show that all of the discharge capacity ratios,obtained with EMD powders on which surface modified layers are formed bya Sr and/or La compound, and a Sr and/or La compound containing Mncompound, are higher than that obtained with untreated EMD powder(Sample No. 1), as improved discharge voltage.

In addition to these, a slight improvement of discharge capacity ratiois seen when the treatment solution is acidified by H₂ SO₄ and when anoxidizing agent of any type is employed, although there is no observableobvious dependency on the type of oxidizing agent in this case also.

Like in the cases of Embodiments-3 and 4, higher apparent densities areobserved with the EMD powders whose surfaces are modified by mixing a Mncompound in the layer. Moreover, apparent from FIG. 7, since the heavyload discharge voltage of the cell (Sample No. 58) employing the EMDpowder whose surface is modified by La compound is higher than thatemploying the untreated EMD powder (Sample No. 1), there is an increaseof discharge capacity up to a voltage of 0.9 V observed. However, noparticular difference in the total capacity is observed.

                                      TABLE 8    __________________________________________________________________________    Sample No.              1  67 68 69 70 10 72 73 74 75 76    __________________________________________________________________________    Composition of    Treatment Solution    H.sub.2 SO.sub.4  (mol/l)              -- 2.0                    2.0                       2.0                          2.0                             2.0                                2.0                                   2.0                                      -- -- --    SrSO.sub.4 (mol/l)              -- 0.2                    -- 0.2                          0.2                             0.2                                0.2                                   0.2                                      0.2                                         0.2                                            0.2    LaSO.sub.4 (mol/l)              -- 0.2                    0.2                       -- 0.2                             0.2                                0.2                                   0.2                                      0.2                                         0.2                                            0.2    MnSO.sub.4 (mol/l)              -- -- 0.2                       0.2                          0.2                             0.2                                0.2                                   0.2                                      0.2                                         -- 0.2    Kind of Oxidizing    Agent    Air (ml/min)              -- -- -- -- -- -- 50 -- -- -- --    O.sub.2  (ml/min)              -- -- -- -- -- -- -- 50 -- -- --    O.sub.3  (ml.min)              -- -- -- -- -- -- -- -- 50 -- --    Na.sub.2 ClO.sub.3              -- ∘                    ∘                       ∘                          ∘                             ∘                                ∘                                   ∘                                      ∘                                         -- --    Na.sub.2 S.sub.2 O.sub.8.2H.sub.2 O              -- -- -- -- -- ∘                                -- -- -- -- --    Apparent Density              2.67                 2.63                    3.01                       2.97                          2.92                             2.92                                2.95                                   3.0                                      3.01                                         2.64                                            2.84    (g/cm.sup.3)    Discharge Capacity              100                 105                    105                       105                          106                             107                                106                                   107                                      105                                         103                                            103    Ratio    __________________________________________________________________________

All of the cells employing the other EMD powder whose surface ismodified by another Sr and/or La compound and by a Sr and/or La compoundincluding the Mn compound showed similar behavior.

FIG. 8 shows the relationship between the pulse discharge cycle countsof LR6-size alkaline manganese batteries employing the EMD powder, whosesurface is modified by depositing a Sr and La compound as its positiveactive material, and the total contents of Sr and La. FIG. 8 also showsthat all of the batteries employing EMD powder whose surface is modifiedby a Sr and/or La compound show definite improvements of pulse dischargecycle counts, and it is particularly effective when the total content ofSr and/or La is in a range from 0.1-10.0 wt %.

In addition to this, an electron microscopic observation made of the EMDpowder whose surface is modified by a Sr and/or La compound and a Srand/or La compound containing Mn compound has shown less surfaceirregularities, like the other EMD powder whose surface is modified. Inaddition to this, higher apparent densities with the surface modifiedEMD powders containing Mn compound (Sample Nos. 68-74 and 76) areobtained, like in the other cases.

<Embodiment-6>

The performance of the positive active material developed fornon-aqueous electrolyte secondary batteries of Sample Nos. 1-76, shownin Embodiments -1 - -5, have been tested.

A cross-section of a coin-type cell developed for the evaluation of thepositive electrode in accordance with an exemplary embodiment of thepresent invention is shown in FIG. 9 wherein 21 is a cell-case made ofstainless-steel anti-corrosive to the organic electrolyte, 22 is a cellcover made of the same material, 23 is the positive electrode of thepresent invention, 24 is a current collector for positive electrode 23made of the same stainless-steel and is spot-welded to the internalsurface of cell-case 21, 25 is negative electrode molded graphite powderand pressed agalnst the inside of cell cover 22, 26 is a separator madeof porous polypropylene, and 27 is an insulating gasket made ofpolypropylene. The evaluation cell coin-type has a diameter of 20 mm andan overall height of 1.5 mm.

The positive active material is prepared by mixing various surfacemodified EMDs prepared in advance with lithium hydroxide (LiOH) at aratio which forms a double oxide of manganese and lithium, LiMn₂ O₄ ofprescribed composition. This mixture is sintered at a temperature of860° C. for 70 hours in an oxidizing atmosphere. The positive electrodecompound is prepared by mixing a conductive agent intopolyvinylidenfluoride acting as a binder at a weight part of 5 to 5, andby mixing this mixture into the obtained positive active material at aweight part of 90, The electrode is prepared by molding the obtainedpositive electrode compound of a prescribed volume on current collector24, and this is dried at a temperature of 150° C. under vacuumconditions, and this is assembled into a cell using a negative electrode25.

Lithium perchlorate, dissolved in a solvent where ethylene carbonate and1,3-dimethoxyethane are mixed at an equal volume obtaining aconcentration of 1 mol/liter, is used as an electrolyte. Since apositive electrode deintercalated lithium-ions electrochemically toelectrolyte by charging after the cell assembly, and intercalated thelithium ions from electrolyte by discharging, it is obvious that thiscomposition functions as a positive electrode material for secondarybatteries.

These evaluation cells were charged up to a voltage of 4.2 V at a rateof 0.2 mA/cm², and then discharged to a voltage of 3.0 V at a rate of0.2 mA/cm² and 1.0 mA/cm² at an ordinary temperature, and the dischargecharacteristics, depending on the difference of discharge rates havebeen determined.

Table 9 shows the ratio of discharge capacity at a rate of 1.0 mA/cm² tothat at a rate of 0.2 mA/cm².

Here, the tests are conducted for Sample Nos. S-2, -9, -13, -14, -22,-31, -50, and -59 employing a concentration of sulfuric acid of 2.0mol/l and a concentration of various sulfates of 0.2 mol/l as acondition of surface modification treatment, and employing sodiumperchlorate as an oxidizing agent. These results are compared with thoseof EMD powder of Sample No. S-1 used as a starting material.

                  TABLE 9    ______________________________________    Sample No.             S-1   S-2   S-9 S-13 S-14 S-22 S-31 S-50 S-59    ______________________________________    Discharge             88    93    89  92   92   91   91   90   90    Capacity    Ratio (%)    ______________________________________

As shown in Table 9, the surface modified samples show better high-ratedischarge characteristics than those obtained by the referenced sampleNo. S-1. Moreover, the same effects could be obtained if the surfacemodification were made on the samples other than those mentioned above.

<Embodiment.-7>

Using the materials of Sample Nos. 1-76 shown in Embodiments-1-5 as apositive active material and zinc as a negative active material, thezinc chloride type carbon-zinc dry cells, shown in FIG. 10, areprepared.

In FIG. 10, there is a positive electrode mix 31, a carbon rod 32 actingas a positive current collector, a zinc can 33, a separator 34, a bottompaper 34A, a plastic sealing cover 35, a positive terminal plate 35A, acover paper 36, a sealer 36A, a negative terminal plate 37, a PVC tube38, and a metal Jacket 39. Positive electrode mix 31 is prepared bymixing said manganese dioxide with acetylene-black at a weight ratio of5:1, adding this into an electrolyte consisting of a mixed solution ofzinc chloride and ammonium chloride, whose main constituent is zincchloride, and by molding.

R20 (D) size carbon-zinc dry cells are prepared this way, and they arecontinuously discharged for a load of 2 Ohms at room temperature (20°C.), and the end voltage decreases to 0.9 V. These results are shown inTable

                                      TABLE 10    __________________________________________________________________________    Sample No.           1  2  5  12 13 14 24 33 52 61    __________________________________________________________________________    Discharge           100              106                 105                    105                       104                          105                             104                                105                                   104                                      104    Duration Ratio    __________________________________________________________________________

As shown in Table 10, carbon-zinc dry cells show better heavy-loaddischarge characteristics when a manganese dioxide having a surfacemodified layer is employed over the cases where the cells employ amanganese dioxide having an unmodified surface layer.

In an example, an alkaline manganese battery prepared by employing anEMD powder having a surface modified layer by a compound consistingmainly of oxide of at least one element selected out of a group of Ti,Co, Ni, Sr, and La, and used as the positive active material, theresistance polarization and the concentration polarization are obviouslylowered at the heavy load and continuous discharge so that dischargecharacteristics of high efficiency can be obtained by the increaseddischarge voltage and the effective capacity. Those cases where a Mncompound is introduced in the surface modified layer are also foundeffective.

The effects observed with the above-mentioned surface layer modificationare not necessarily limited only to the alkali manganese batteries. Byconducting a surface modification by depositing a compound of at leastone element selected from the group consisting of Ti, Co, Ni, Sr, and Laon the surface of not only EMD but CMD and natural manganese dioxide(NMD), and by using this as a positive active material, thosemodifications can also be applied to Leclanche type and zinc chloridetype, carbon-zinc dry batteries.

Moreover, by applying a heated dehydration treatment at a temperaturefrom 350-450° C. to said surface modified manganese dioxide powder, thepositive active material for the Li/MnO₂ system, an organic electrolytelithium primary battery having high rate discharge characteristics canbe obtained.

Furthermore, by using a manganese oxide on which a surface modifiedlayer is formed by depositing a compound of at least one elementselected from the group consisting of Ti, Co, Ni, Sr, and La on thesurface of LiMnO₂ or LiMn₂ O₄ powder which is a double oxide of Mn andLi and by repeating the deintercalation and intercalation of Li bycharge and discharge at the positive electrode, ever better charge anddischarge characteristics can be obtained.

In these embodiments, although there is an example using a sulfateaqueous solution as the treatment solution for surface modification thetreatment solution of the present invention is not necessarily limitedto using sulfates.

When chlorides or nitrates, etc. are used as the positive activematerial of the battery after the treatment, the use of these salts cannever be disturbed by the possible introduction of minute anionscontained in the treatment solution. For instance, it may be well knownthat chloride solution is used as the treatment solution acting as thepositive active material for carbon-zinc dry batteries wherein NH₄ Cland/or ZnCl₂ are used as electrolytes.

Thus, batteries may be produced which use a manganese oxide where thesurface of manganese oxide powder consisting essentially of MnO₂, Mn andLi of a double oxide is modified by the deposition of a compoundconsisting mainly of an oxide of at least one element selected from thegroup consisting of Ti, Co, Ni, Sr, and La as its positive activematerial, and a compound made mainly of a Mn oxide, by using a solutionin which is dissolved a salt of at least one element selected from thegroup consisting of Ti, Co, Ni, Sr, and La to which a Mn salt is added.

And this is highly effective to improve the heavy load continuousdischarge characteristics of primary batteries such as carbon-zinc drybatteries, alkaline manganese batteries, and Li/MnO₂ system organicelectrolyte lithium batteries.

Furthermore, further improvements of high-rate charge and dischargecharacteristics with the lithium-ion secondary batteries can also beexpected. These could be made possible by the reduction of resistancepolarization and/or concentration polarization of the positive activematerial used therein.

While preferred embodiments of the invention have been shown anddescribed herein, it will be understood that such embodiments areprovided by way of example only. Numerous variations, changes, andsubstitutions will occur to those skilled in the art without departingfrom the spirit of the invention. Accordingly, it is intended that theappended claims cover all such variations as fall within the spirit andscope of the invention.

What is claimed:
 1. A method of manufacturing a positive active materialfor a battery comprising the steps of:providing a treatment solution ofa first salt of at least one element selected from the group consistingof titanium, cobalt, nickel, strontium and lanthanum; providing amanganese oxide powder of a manganese compound including manganese andoxygen, said manganese oxide powder comprised of a plurality of grains,each grain having a surface; and depositing a surface modification layeressentially comprising an oxide of at least one element selected from agroup consisting of titanium, cobalt, nickel, strontium and lanthanum,onto each said surface by dispersing said manganese oxide powder withinsaid treatment solution.
 2. A method of manufacturing a positive activematerial for a battery according to claim 1, wherein said manganeseoxide powder is formed by adding a manganese salt to said treatmentsolution.
 3. A method of manufacturing a positive active material for abattery according to claim 1, wherein said first salt comprises at leastone salt selected from the group consisting of sulfate, nitrate, andchloride salts.
 4. A method of manufacturing a positive active materialfor a battery according to claim 2, wherein said first salt comprises atleast one salt selected from the group consisting of sulfate, nitrate,and chloride salts.
 5. A method of manufacturing a positive activematerial for a battery according to claim 1, wherein an acidity of saidtreatment solution is maintained during said step of depositing asurface modification layer.
 6. A method of manufacturing a positiveactive material for a battery according to claim 2, wherein an acidityof said treatment solution is maintained during said step of depositinga surface modification layer.
 7. A method of manufacturing a positiveactive material for a battery according to claim 3, wherein an acidityof said treatment solution is maintained during said step of depositinga surface modification layer.
 8. A method of manufacturing a positiveactive material for a battery according to claim 4, wherein an acidityof said treatment solution is maintained during said step of depositinga surface modification layer.
 9. A method of manufacturing a positiveactive material for a battery according to claim 1, further comprisingadding to the treatment solution at least one oxidizing agent selectedfrom the group consisting of air, oxygen, ozone, sodium perchlorate, andsodium persulfate during said step of depositing a surface modificationlayer.
 10. A method of manufacturing a positive active material for abattery according to claim 2, further comprising adding to the treatmentsolution at least one oxidizing agent selected from the group consistingof air, oxygen, ozone, sodium perchlorate, and sodium persulfate duringsaid step of depositing a surface modification layer.
 11. A method ofmanufacturing a positive active material for a battery according toclaim 3, further comprising adding to the treatment solution at leastone oxidizing agent selected from the group consisting of air, oxygen,ozone, sodium perchlorate, and sodium persulfate during said step ofdepositing a surface modification layer.
 12. A method of manufacturing apositive active material for a battery according to claim 4, furthercomprising adding to the treatment solution at least one oxidizing agentselected from the group consisting of air, oxygen, ozone, sodiumperchlorate, and sodium persulfate during said step of depositing asurface modification layer.
 13. A method of manufacturing a positiveactive material for a battery according to claim 5, further comprisingadding to the treatment solution at least one oxidizing agent selectedfrom the group consisting of air, oxygen, ozone, sodium perchlorate, andsodium persulfate during said step of depositing a surface modificationlayer.
 14. A method of manufacturing a positive active material for abattery according to claim 6, further comprising adding to the treatmentsolution at least one oxidizing agent selected from the group consistingof air, oxygen, ozone, sodium perchlorate, and sodium persulfate duringsaid step of depositing a surface modification layer.
 15. A method ofmanufacturing a positive active material for a battery according toclaim 7, further comprising adding to the treatment solution at leastone oxidizing agent selected from the group consisting of air, oxygen,ozone, sodium perchlorate, and sodium persulfate during said step ofdepositing a surface modification layer.
 16. A method of manufacturing apositive active material for a battery according to claim 8, furthercomprising adding to the treatment solution at least one oxidizing agentselected from the group consisting of air, oxygen, ozone, sodiumperchlorate, and sodium persulfate during said step of depositing asurface modification layer.
 17. The method according to claim 1, whereinsaid manganese compound further includes lithium.
 18. The methodaccording to claim 17, wherein said manganese compound comprises one ofmanganese dioxide, LiMnO₂ and LiMn₂ O₄.
 19. The method according toclaim 1, further comprising the step of drying said powder after saidstep of depositing a surface modification layer.